1. Field of the Invention
The present invention relates to a system for structurally lining pipes, tanks or other cylindrical, oval or otherwise curve-shaped structures and a method for applying the structural lining to these structures. The application of this invention is not limited to pipes and tanks and not limited to cylindrical, oval or curve-shaped structures. Specifically, the invention is a method of securing a series of hoop-shaped strips of unidirectional carbon fiber material circumpherentially to an interior surface of a pipe so that sides of each strip abut the side of an adjacent strip. The unidirectional carbon fiber material is factory manufactured and cured with the carbon fibers oriented in a single direction. The strips are secured to the pipe by first applying an adhesive to the interior surface and then releasing a coiled strip so that it springs open to press itself against the interior surface. If ends of the strip overlap, additional adhesive is applied between the overlapping portions of the ends. A final coating of epoxy or other suitable coating may be applied to the strips to complete the installation.
When securing the strips to the interior surface of the pipe, it may be desirable to have one end of each strip overlap its opposite end and also to stagger the junctions formed by the ends of strips. The strips should be applied to the interior surface of the pipe so the end junctions of adjacent strips are staggered within the pipe, i.e. so that the end junctions of adjacent strips do not line up linearly along a longitudinal axis of the pipe.
2. Description of the Related Art
Pipes used in certain types of installations, such as for example a makeup water supply pipe to a nuclear power plant, are large in internal diameter, must withstand a certain amount of pressure, and must be dependable since failure of the pipe presents unacceptable risk.
For example a typical pipe might be constructed of a steel can embedded between an interior layer and an exterior layer of pre-stressed concrete and might have an internal diameter in the range of 8-12 feet.
These types of pipe experience significant regional problems where they are exposed to xe2x80x9chot soilsxe2x80x9d. xe2x80x9cHot soilsxe2x80x9d are soils that are comprised of or contain specific corrosive components, such as acids, caustics, or salts, that can greatly accelerate the corrosion of pipe, attacking concrete, steel cans, reinforcing bars or wire. Unlike sewer pipes where the corrosion takes place from the inside out, in xe2x80x9chot soilsxe2x80x9d chlorides from the soil enter the concrete matrix of the pipe and attack then wire contained in the pre-stressed concrete. This may have been accelerated due to the lack of or improper application of cathodic protection.
As steel oxidizes, it expands, creating pressures that further open and widen cracks in the external layer of concrete and accelerate the deterioration of this layer of the pipe. Eventually the can begins to corrode and pinholes develop. The pinholes permit water to travel through the inner concrete line, through the pinholes and out the pipe via the deteriorated external layer. Once this occurs, it only takes a very short time, possibly only weeks or months, until the pipe is weakened to the point of permitting a rupture.
Current methods for addressing this problem include (1 replacement of the entire pipe, (2 installing a slip lining within the pipe, (3 inserting a cured-in-place pipe, also referred to as a CIPP lining or (4 lining the pipe with carbon cloth. A more complete discussion of these current methods is contained in a paper entitled xe2x80x9cUse of Structural Lining Systemsxe2x80x9d published in the papers of the 7th International Conference on Nuclear Engineering held in Tokyo, Japan on Apr. 19-23, 1999 and sponsored by the American Society of Mechanical Engineers, et.al.
Replacing large pipes is slow, costly and unless different materials are used, the problem is destined to reoccur. The cost to install a replacement pipes is generally prohibitive, but the cost associated with the down time of the facility associated with such a replacement is generally even more expensive than the actual costs of replacing the pipe. For this reason, replacement of the entire pipe is generally not a viable option.
The second method currently employed for addressing this problem is to install a slip lining within the pipe. Using a slip lining, folded form liner, or sock liner reduces the interior diameter of the pipe and as the pipe grows in size, becomes increasingly difficult to handle.
Employing a CIPP lining may be an acceptable technical solution, but the costs are very high and, for pressure pipe, the technology is limited to pipes about 42 inches in diameter.
Lining a pipe with carbon cloth can work, but installation is extremely labor intensive, slow, costly, and wasteful of materials. To install carbon cloth to the interior surface of a pipe, the interior of the pipe is first hydro-blasted and then workers manually mix and trowel or roll the epoxy mortar that is used as the adhesive onto the interior surface of the pipe. Then the workers apply sections of carbon cloth to the interior surface, similar to the way wallpaper is hung on a wall of a building. The carbon cloth must be rolled out by hand with a great deal of effort to ensure that all of the carbon fibers are wetted. Also, the size of the cloth pieces that may be applied is limited because of the weight and handling considerations. Limiting the size of the cloth pieces limits the effectiveness of what should be a continuous fiber lining.
One problem inherent in lining a pipe with carbon cloth by this method is that any epoxy mixture that is not used in a short period of time must be discarded. Another problem is that a large amount of the epoxy drips off of the interior surface during the application of the carbon cloth, creating additional waste and creating messy and difficult working conditions for the workers. Also, when the carbon cloth is wet, it becomes very heavy and as the epoxy loses its thixotropic properties or viscosity as temperatures change or it cures, it is likely that some of the carbon cloth will fall off of the interior surface.
The present invention addresses these problems by providing a structural lining system for application to the interior surface of a pipe and a method for applying the structural lining. First hydro blasting cleans the interior of the pipe. Next, a layer of adhesive is sprayed onto the interior of the pipe. The, strips of previously coiled unidirectional carbon fiber material are applied to the interior of the pipe by allowing the strips to uncoil against the interior of the pipe so that side edges of the strips abut the side edges of adjacent strips. If ends of the strips overlap, additional adhesive, either the same or a different type of adhesive than that used on the interior surface, is applied between the overlapping portions of the ends. Finally, a spray on coating is applied over the strips. This coating forms and internal liner that protects the unidirectional carbon fiber material from abrasion, provides a very low friction monolithic liner, and is light in color to allow for easy visual inspections in the future.
The present invention does not waste materials, and it does not create a messy work environment for the installation workers. The present invention is easy to apply, even to large diameter pipes, employing only a relatively small number of installation workers. The present invention can be installed quickly and at relatively low cost. The present invention increases the tensile strength of the pipe without a significant decrease in the interior diameter of the pipe. Finally, the present invention provides a permanent solution to the problem.
The present invention is a structural lining system for application to the interior surface of a pipe and a method for applying the structural lining. The structural lining is applied to the interior of a pipe by first cleaning the interior of the pipe by hydro blasting. Next, a layer of adhesive is sprayed onto the interior of the pipe to form an adhesive layer. Although a number of adhesives might function, a moisture-insensitive, 100% solids epoxy functions best because of its superb strength and excellent adhesive qualities. It can also be made thixotropic to permit an adhesive layer thick enough to compensate for minor irregularities in the pipe. On smooth pipe, an epoxy layer of 0.5 mm to 1.0 mm might be typical.
Then, strips of previously coiled unidirectional carbon fiber material are applied to the interior of the pipe by allowing the strips to uncoil. Unidirectional carbon fiber fabric may be obtained as CARBOLAM HR available from Epsilon Composite, 5, Route de Hourtin, 33340 Gaillan, France.
The strips uncoil on their own in an attempt to return to a flat configuration, against the curved interior of the pipe so that side edges of the strips abut the side edges of adjacent strips. It may be desirable to overlap the two ends of each of the strips to provide additional strength to the pipe. If ends of the strips are to be overlapped, additional adhesive, either of the same or of a different type than the adhesive used on the interior surface, is applied between the overlapping portions of the ends.
Finally, a spray on coating, preferably an epoxy coating, is applied over the strips. This final coating forms an internal liner that protects the unidirectional carbon fiber material from abrasion, provides a monolithic liner with very low friction, and is light in color to allow for easy visual inspections in the future.